1. Technical Field
The present invention relates to an image forming apparatus and an image forming method with which it is possible to continuously form images amounting to plural pages while switching plural developers which hold toner of the same color.
2. Related Art
Known image forming apparatuses equipped with multiple developers includes such an apparatus which forms full-color images using multiple developers which hold toner of different colors from each other and while switching from one developer to the other and forms monochrome images using one of such developers. In the image forming apparatus described in JP-A-2005-003759 for instance, a rotary developer seats four developers which respectively hold yellow toner (Y), magenta toner (M), cyan toner (C) and black toner (K), and this apparatus is capable of executing a color printing mode of superimposing on an intermediate transfer belt toner images of the respective colors which have been formed while switching the developers and accordingly forming a full-color image and a monochrome printing mode of forming a monochrome image fixing the developer to use to the black developer.
Further, in this image forming apparatus, images are formed at different positions on the intermediate transfer belt between the color printing mode and the monochrome printing mode. In the color printing mode, since respective color images need be superimposed one atop the other while switching from one developer to the other in, a particularly wide inter-image area is provided for every revolution of the intermediate transfer belt. On the contrary, for the monochrome printing mode which does not require switching of the developers, images are equidistant from each other.
Now, considering how this type of image forming apparatus is typically used, even if an apparatus is capable of forming a full-color image, the apparatus is often used to form a monochrome image. This has given rise to a thought that this type of apparatus may mount plural developers which hold toner of the same color and form monochrome images while switching from one developer to the other (which mode of use will be hereinafter referred to a “multiple monochrome use”).
However, almost no consideration has been given to the issue of how the inter-image gaps should be set when one attempts to continuously form plural images using such an image forming apparatus which realizes the multiple monochrome use. For instance, as for the conventional image forming apparatus described above, while the color printing mode requires switching from one developer to the other for every revolution of the intermediate transfer belt, the gaps between images are determined based on the premise of not switching the developers for the monochrome printing mode. As these assumptions are invalid for an image forming apparatus which permits the multiple-monochrome use, application of this conventional technique to an image forming apparatus which permits the multiple-monochrome use will not necessarily result in an optimal result.